This chapter is from the book

This chapter is from the book

Choosing Your Working Spaces

You set up your working spaces in the Color Settings dialog (Edit > Color Settings; see Figure 4-3). The simplest way to use Color Settings is to choose a preset from the Settings pop-up menu. Because the choices in that pop-up menu are presets, when you choose one it changes many options in the dialog. If one works for you as it is, just choose it and you're done. Or you can choose a preset as a good starting point, and then fine-tune it.

For RGB, remember that working spaces are just defaults, affecting only images that aren't tagged. If most of the images you open already have correct profiles embedded in them, you won't have to obsess over getting the working spaces exactly right. That said, it's best to pick one for each color mode that matches your primary workflow, such as prepress or Web design. For CMYK, there are still workflows that don't require profiles to be embedded in images, and in those workflows it's important that the CMYK working space be set to the profile for your press conditions.

About the Built-In RGB Working Spaces

The RGB working spaces built into Photoshop are designed to provide a good environment for editing images. As such, they have two important properties that aren't shared by the vast majority of device spaces.

Gray balance. The built-in working spaces are gray-balanced, meaning simply that equal amounts of R, G, and B always produce a neutral gray. This is hardly ever the case with device (scanner, camera, display, printer) spaces. Since one of the easiest ways to bring color into line is to find something that should be neutral and make it so, gray balance is an extremely useful property.

Perceptual uniformity. The built-in working spaces are approximately perceptually uniform, meaning that changing each channel's numeric values in the image by the same increment results in about the same degree of visual change, no matter whether it's in the highlights, the midtones, the shadows, the pastels, or the saturated colors. Again, device spaces generally don't work that way.

All color-space conversions entail some data loss, but the conversion from capture (camera or scanner) to working space is, in our experience, invariably worthwhile, and when it's done in 16-bit/channel mode, the loss is so trivial it's just about undetectable. Even in 8-bit/channel mode, you're likely to produce much better results editing in a working space rather than a device space. The idealized properties of the built-in RGB working spaces also makes them useful for creating and archiving master images, from which you can make copies that you convert for specific types of output.

Why Not Just Use Lab? After all, Lab is, by design, a device-independent, perceptually uniform color space. But Lab has at least two properties that make it less than ideal as a standard editing space.

First, Lab is pretty nonintuitive when it comes to making color corrections—small adjustments to a* and b* values often produce large changes in unexpected directions. A bigger problem, however, is that Lab, by definition, contains all the colors you can see, and as a corollary, it also contains many "colors" you can't see.

When we use 8 bits per channel to represent this whole range of color, the distance from one value to the next becomes uncomfortably large. And since any real image from a scanner or digital camera contains a much smaller range of color than Lab represents, you waste bits on colors you can't capture, display, print, or even see. If you work with 16 bit/channel images, the gamut problem is much less of an issue, but editing in Lab is still not particularly friendly, and conversions from capture space to Lab generally involve more data loss due to quantization error than the conversion to RGB working spaces.

Choosing an RGB Working Space

If you're doing prepress or other high-quality printing, Adobe RGB is the one working space that's big enough not to clip U.S. Sheetfed Coated v2 (a typical CMYK color space) very much, and yet it is also constrained enough to work well as an editing space for 8 bit/channel images. If your work is aimed primarily at the Web or video, sRGB is the natural choice. If you print to printers with larger gamuts than a CMYK press has, and you're comfortable with 16 bit/channel editing and handling color space conversions, ProPhoto RGB is a definite option for you.

David likes to keep things simple and uses Adobe RGB virtually all of the time. Conrad uses different working spaces depending on the project. It isn't absolutely necessary to load these as working spaces in Color Settings—you can always use the Assign Profile command (see "Assign Profile" later in this chapter) to assign a profile other than the working space to an image—but if you're going to be working with a bunch of images in the same space, it makes life slightly easier to load that space as the working space.

Choosing a CMYK Working Space

Unlike RGB working spaces, which may be entirely abstract and not based on any real device, CMYK working spaces always reflect some real combination of ink (or toner, or dye) and paper. The ideal situation is to have a custom ICC profile for the specific CMYK process to which you're printing. In the real world, however, some shops are ahead of others in achieving this workflow. If you do have a custom ICC profile for your CMYK print process or for an industry-standard proofing system such as Kodak Approval or Creo Spectrum, click the More Options button and load that profile into the CMYK pop-up menu in the Color Settings dialog.

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Some Mac users naturally gravitate to using Apple RGB as a working space because it has the word Apple in it. This is wrong. Apple RGB is based on the early 13-inch Apple RGB High-Resolution monitor (640 by 480 pixels), which hasn't been produced in more than 15 years. Any of the default RGB working spaces is better. ColorMatch RGB also represents a long-dead brand of CRT monitor.

By default, your choices of CMYK working space are limited to the press profiles that are installed by Photoshop, plus Custom CMYK, which users of older versions of Photoshop may recognize as the old "Built-in" panel of Photoshop 5's CMYK Setup. Mac users also get the option to choose ColorSync CMYK, which, with the advent of Tiger (Mac OS X 10.4), is hardwired to Generic CMYK, a profile that represents no printing condition known to humankind and so is best ignored.

If you're using an accurate CMYK profile, either as a working space or as a profile in tagged CMYK images, you shouldn't have to worry about dot gain, gray component replacement (GCR), and so on. Because a properly created profile represents the output conditions, all output characteristics should already be accounted for by the profile. Choose Load Custom CMYK from the CMYK working space pop-up menu to select your CMYK profile.

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When you build your own CMYK profiles for a press or proofer, it's always a good idea to build a family of profiles with different black generations. Some profiling tools will even let you take an existing profile and regenerate it with new black generation settings.

If you're still working with a printer who is more comfortable with the old-style Photoshop CMYK setups, they're still available. Choosing Custom CMYK from the CMYK pop-up menu opens the Custom CMYK dialog; the settings for that dialog should be supplied by your printer. Today's profiling technologies are far superior to the old manual methods, so use a CMYK profile when available.

Choosing a Gray Working Space

Grayscale profiles are independent of RGB or CMYK. However, note that grayscale profiles contain only tone reproduction information; they have no information about the color of the black ink or of the paper.

When Color Settings is displayed with Fewer Options, you can choose among grayscale dot gains of 10, 15, 20, 25, or 30 percent, depending on your printing conditions. You can also choose either gamma 1.8 or 2.2, which are good choices for grayscale images destined for the screen or for unknown printing conditions. Of course, there's nothing to prevent you from using these gamma values for print images, or the dot-gain curves for onscreen use, but generally speaking, gammas are designed for onscreen use and dot-gain curves are designed for print.

When to Reveal the Hidden Options

Photoshop presents a short list of options in the Color Settings dialog by default, to keep from overwhelming you with choices. If you click More Options, you'll not only see the dialog expand with additional features, but you'll find more profiles listed in the Working Space pop-up menus. Some of them are holdovers from previous versions of Photoshop, included only to support old images you might open. The rest are all the profiles you've installed on your computer, such as profiles for your desktop printer.

For RGB, most people are best served by using one of the working spaces on the "short list" in the shorter Color Settings dialog. The need to use or define a custom RGB working space should be rare.

As we've discussed, for CMYK, you do want to have a custom CMYK profile for your printing conditions. You don't need to click More Options to see your custom CMYK profile, since you can select the profile straight from your disk by choosing Load CMYK.

Custom Gray and Spot Color Spaces

As with Custom CMYK, you can choose Custom Dot Gain (see Figure 4-4) from the Gray pop-up menu in the Working Spaces section of the Color Settings dialog. This is necessary only if you're doing grayscale work and don't already have a grayscale profile to load. Two reasons to edit a custom gray working space are to enter custom dot-gain values or to load the black channel from your CMYK profile so that you can use it for grayscale images. (There's also a Custom Gamma option, but it's rarely needed.) To save your gray settings as a grayscale profile, choose Save Gray from the Gray working spaces pop-up menu.

Figure 4-4 To build a custom dot-gain curve, enter the measured dot area for a swatch. You can enter a single value for the 50 percent dot or take more measurements to increase accuracy.

The Custom Dot Gain command in the Spot working spaces pop-up menu is essentially the same as the grayscale option of the same name, and you can use it if you want a dot-gain curve other than the many already available in that pop-up menu. As with grayscale settings, spot color settings know nothing about the actual color of the ink and paper, and they contain no information about the way the spot ink interacts with other inks.